The present invention relates to an imaging material of the type in which a layer of photosensitive microcapsules is provided on a photographic support and, more particularly, to an improved imaging material in which the microcapsules contain a solid diluent in the internal phase.
U.S. Pat. Nos. 4,399,209 and 4,440,846, assigned to The Mead Corporation, describe transfer and self-contained imaging systems in which the imaging sheet comprises a support carrying a layer of photosensitive microcapsules. The microcapsules contain an internal phase which includes a photosensitive composition which undergoes a change in viscosity upon exposure to actinic radiation. The photosensitive composition is typically a photohardenable composition such as a composition which undergoes free radical addition polymerization. The imaging materials can be used to form dye images or light scattering images. Most typically an image-forming agent, such as a substantially colorless electron donating compound, which generates a colored dye upon reaction with a developer, is encapsulated with the photosensitive composition in the internal phase of the microcapsules. In self-contained imaging systems, the co-reactive developer material is provided on the surface of the imaging sheet with the photosensitive microcapsules. In transfer imaging systems the developer is provided on a separate sheet.
To form images, the above described imaging sheets are image-wise exposed to actinic radiation and subjected to a uniform rupturing force whereupon the microcapsules rupture and image-wise release the internal phase. In the case of microcapsules containing a photohardenable composition, the internal phase is released in the areas which are not exposed to actinic radiation or areas which are underexposed. In these areas, the microcapsules rupture and the internal phase remains sufficiently fluid to be released from the microcapsules. Thus, in these areas the image-forming agent associated with the microcapsules can react with the developer material and produce a color image. In the fully exposed areas, the microcapsules are either incapable of rupturing or, if they do rupture, the internal phase is too viscous to be released from the capsules. A detailed explanation of these imaging materials and the process whereby images are formed can be found in both of the aforementioned patents.